The invention relates to a dual-polarized multiband antenna.
Dual-polarized multiband antennas are used for transmitting (or receiving) two linear polarizations which are aligned at right angles to one another and may be aligned, for example, vertically and horizontally. However, in practice those operational cases in which the polarizations are aligned at +45.degree. and -45.degree. to the vertical (or to the horizontal) are also of particular importance. In the case of dual-polarized multiband antennas, said antennas are operated in at least two frequency bands, as a rule with two mid-frequencies which are well apart from one another. In this case, the upper mid-frequency should be at least 1.5 times the lower mid-frequency.
With such a large frequency separation, two antenna modules or antenna arrays arranged physically separately from one another are normally used, namely for transmitting and receiving in the one frequency band range and for transmitting and receiving in the other frequency band range (frequency band).
Dual-polarized antennas as such are known. They are used for simultaneously transmitting or receiving two orthogonal polarizations. In this case, such radiating element arrangements may comprise, for example, a plurality of elements in the form of dipoles, slots, planar radiating elements or so-called patch radiating elements, as are known, for example, from EP 0 685 900 A1 or from the prior publication "Antennen [Antennas], Part 2, Bibliographical Institute, Mannheim/Vienna/Zurich, 1970, pages 47 to 50". Dipoles arranged in a cruciform shape (cruciform dipoles) or double-dipole arrangements which have a square structure in plan view (dipole square) are preferably used for the dipole arrangements.
Dual-polarized antennas are furthermore also known, for example, from WO 98/01923.
Dual-polarized antennas are likewise known from the publication "Dual-Frequency Patch Antennas", IEEE AP Magazine, page 13 et seq. This document describes dual-polarized multiband antennas which use different patch structures, but have a series of disadvantages. For example inadequate decoupling for both polarizations is thus typical. The described designs allow only one horizontal/vertical position alignment. For example, it is impossible with simple means to produce a multiple array arrangement with a +45.degree./-45.degree. alignment.
Further antenna forms which have become known once again use two antennas arranged separately one above the other for the respective frequency range.
Finally, for example, a microstrip antenna is known from DE-A1 362 079, which is suitable for transmission in two frequency ranges, but with only one polarization. This antenna arrangement not only has a low gain, but it has also been found to be disadvantageous that the polar diagrams which can be achieved with such an antenna cannot be used for array antennas.
In contrast, the object of the present invention is to provide a dual-polarized multiband antenna, in particular a so-called X-polarized multiband antenna, which avoids the disadvantages mentioned above. This antenna is thus intended to be operable in at least two frequency ranges, which are preferably well apart from one another. Furthermore, it is preferably intended to have a high level of decoupling between the two polarizations.
The object is achieved according to the invention in accordance with the features specified in
Claim 1 and Claim 2. Advantageous refinements of the invention are specified in the dependent claims.
The dual-polarized multiband antenna according to the invention has previously unimagined advantages and features. These advantages relate not only to the decoupling, the bandwidth and the sensitivity, but also to the flexibility of the antenna. The antenna according to the invention is distinguished by the fact that it has at least one radiating element module in the form of a cruciform dipole and like a dipole square, which is located in front of a reflector and which can be operated with dual polarization in two alignments positioned at right angles to one another which, as a rule, that is to say preferably, assume an alignment of +45.degree. and -45.degree. to the vertical or horizontal. This radiating element module in the form of a dipole square can be operated in a lower frequency range. However, according to the invention, further dipoles are now provided for operation in a second upper frequency band with dual polarization, with the further dipoles being arranged within the dipole square. In addition, the further dipoles are preferably in the form of a cruciform dipole. The dipole elements are in this case aligned parallel or at right angles to the dipole elements of the dipole square and thus, in the case of an X-antenna, likewise have an alignment of +45.degree. and -45.degree. to the vertical or horizontal.
A development of the invention provides that the respective holder for the dipoles of the lower frequency range, which at the same time operate as so-called balancing, are designed and/or arranged and/or dimensioned such that, in consequence, no resonance occurs in the upper frequency range, or at least no relevant resonance occurs in the upper frequency range.
It has furthermore been found to be advantageous if, depending on the frequency-dependent wavelength associated with them, the height of the dipoles are [sic] arranged such that they are not more than one wavelength away from the reflector or the reflector plane. Advantageous values are in a range from 1/8 to 1/2 of the respective operating wavelength.
Above all, it is surprising in the case of the antenna according to the invention that, firstly, it has a broad bandwidth and, secondly, at the same time has a high level of decoupling between the two polarizations. It is also distinguished above all in that, with the antenna according to the invention, it is possible to ensure that the horizontal half beamwidths of the two radiating element modules are identical or virtually identical, that is to say essentially of the same magnitude, in both the lower and the upper frequency band ranges.
The advantages according to the invention can, above all, be achieved even when the antenna according to the invention is constructed not only with a dipole square and a cruciform dipole arranged in it, but like an antenna array with a plurality of such square dipoles, each having further internal dipoles, preferably in the form of cruciform dipoles. With this embodiment in particular, it is possible to provide a further radiating element module for transmission of the upper frequency band between each of the two dipole squares for transmitting and receiving the lower frequency band.
However, this further radiating element module is then preferably not in the form of a cruciform dipole, but likewise in the form of a dipole square.